Information storage device



May 31, 1966 J. F. DREYER 3,253,497

INFORMATION STORAGE DEVICE Filed oct. so. 1961 re er United States Patent C) 3,253,49 INFORMATION STORAGE DEVICE John F. Dreyer, Cincinnati, Ohio, assignor to Polacoat Incorporated, Blue Ash, Ohio Filed Oct. 30, 1961, Ser. No. 148,389 Claims. (Cl. 88-1) This invention relates to an information storage system, and relates particularly t-o an information storage system having a tenebrescent storage unit.

Tenebrescence is thatproperty of certain natural andsynthetic materials of reversibly darkening and bleaching under suitable radiation. A scotophor, as the term is used herein, is a material showing the property of tenebrescence.

According to the present invention, tenebrescent materials, or scotophors, are employed in an information storage unit or cell in a system for the deposit, storage, and retrieval of information.

The darkening and bleaching of tenebrescent materials has been recognized earlier in the art. For example, it isknown that by exposure of a scotophor to high-energy radiation (e.g. nuclear particle bombardment, X-rays, cathode rays or light of short wavelengths), the absorption characteristics of the scotophor can be changed, i.e. the scotophor can bechanged in color. By illumination of the scotophor with visible light, the color change in the scotophor can be-detected or read However, since the return of the scot-ophor to its first or unirradiated state is also -brought about by irradiation of the colored material with these long wavelengths, which are abs-orbed in part, viewing of the scotophor causes bleaching or erasing of the scotophor and loss of the colored portions thereof.

According to the present invention, it has been discovered that the erasing and reading of a scotophor which has been changed in color wholly or lin part by high-energy radiation (whether particulate or electromagnetic) causing a color change in the material can beeffected by light of different intensities or with light of 'different wavelengths. In this manner, the crystal may be read or viewed without susbtantial bleaching or erasing of the information (color) stored therein. The latter system employing different wavelengths offers particular advantages, since control of the Wavelength of light is more easily effected, for example by the use 'of filters, than is the control of the intensity of light-beams.

A better understanding of the present invention and of its many advantages will be had by referring to thevaccompanying drawing, which is a perspective schematic View of the system -of the invention. The figure shows a tenebrescent information storage unit as opaque body 11 consisting in whole or in 'part of a tenebrescent material. Unit 11, for example, may be an opaque tenebrescent crystal, or may comprise a suibstrate of any suitable material having a coating of tenebrescent substance formed thereon. The coating may ybe continuous and comprise a` finely-divided tenebrescent material in a suitable adhesive binder, for example, or` the tenebrescent material may be applied by owin-g onto a base while in a fluid condition. The coating may also be discontinuous and comprise discrete islands of a tenebrescent composition applied to a base in a suitable fashion.

The information storage unit 11 may also be pellucid, i.e. transparent or translucent, rather than opaque, and may consist in whole or in part of a pellucid tenebrescent substance, e.g. a pellucid tenebrescent crystal, or a pellucid' tenebrescent material in combination with a pellucid base material to which it is aixed.

The system of the invention also contains writerscanner means, shown in the figure as cathode ray tube 12 connected with conventional input and sweep circuits and equipped with Schmidt optics 13,'which play a modulated ice scanning beam of activiating radiation across the face of unit y11. This radiation is of a high energy suitable to cause coloring of the scotophor, i.e. to cause the scotophor to absorb in wavelength regions outside those in which it normally absorbs. If the radiation is electromagnetic, high energy will be synonymous with short wavelength.

Also adapted `to`play a modulated beam of erasing radiation of suitable wavelength across the face of unit 11 are eraser-scanner means, also shown in the figure as cathode ray tube 14 equipped with Schmidt optics 15. The wavelengths emanating from the erasing means are suitably at the absorption peak of the darkened scotophor, for example, which are the wavelengths most effective in causing bleaching of the scotophor.

The system also contains a source of light flooding entire unit 11 withl light having neutral or non-erasing and non-writing characteristics, shown in the figure as oodlight 16 and filter 17.

Finally, the system contains reader-scanner means, shown in the figure as icon-oscope 18, connected with conventional output and sweep circuits.

In operation, writer-scanner means 1'213 of the figure are used to play modulated beam 19 across the surface of unit 11, causing selective color change in the tenebrescent material, indicated as dark spots 20 in the figure. It is 'evident that by proper modulation of the writing beam a preselected pattern of color change can be produced on the surface of unit 11. This pattern is indicated in the ligure as one in which dark spots 20 are produced between selected intersections of an imaginary grid of horizontal and vertical lines. This pattern is selected only for ease of illustration, and it is clear that any regular or irregular pattern, e.g. a pictorial image, may be produced in unit 11 by writing beam 19.

Similarly, byplaying modulated beam 21 of an appropriate erasing wavelength over the face of unit 11 from eraser-scanner means 14-1'5, a predetermined pattern of decolorization can be effected in storage unit 11, either concurrently or intermittently with the writing operation.

The information (i.e., the color pattern) present in unit 11 at'a given time is read, i.e., viewed or sensed in some other manner, by illuminating the information storage pattern in unit 11 with radiation of a neutral character, that is radiation, e.g. light, of an intensity or wavelength causing substantially no erasing or writing in the crystal, but which is differently absorbed, transmitted, and/or reected by darkened and bleached portions 'respectively of the scotophor of unit 11. Conveniently this viewing light 22 is produced by floodlightfilter combination 16-17. Detection of the colored and uncolored portions of unit 11, under the illumination 22, 'is effected by appropriate detecting means, shown in the figure as reader-scanner iconoscope 18.

Numerous variations of the system described above can be employed, and are comprised within the scope of this invention. For example, unit 11, shown in the figure as opaque, may be pellucid (i.e., transparent or translucent) for which detection of colored and uncolored portions can be effected by transmitted, rather than by reflected, radiation. In this case, illuminating beam 22 is suitably cast through unit 11, and the Iter-oodlight combination 16'1 7 is positioned on the far side of unit 11, a-s shown by the broken lines of the figure. If unit 11 comprises any non-tenebrescent substances, e.g., a base for a tenebrescent coating, the substances -are suitably chosen also to be pellucid.

a broad-field reader can be etected by a movable scanning beam of illuminating radiation.

Similarly, the icathode ray, tubes and Schmidt optical systems employed in writer-scanner means i12-13 and eraser-scanner means 14-15 can be replaced by other scanning means known to the art which play a rnodulated beam of suitable radiation across the surface of unit 11. In the cathode ray tubes 12 and 14 shown in the figure, radiation, e.g., light of an appropriate writing or erasing wavelength can be generated by proper selection of the phosphors used in the construction of the cathode ray tubes. Alternatively, light of suitable writing or erasing wavelengths may be obtained by interposing lters in light beams 19 and 21, whether these beams are generated by cathode ray tubes or by other means.

Although this specification speaks of colored and uncolored portions of a scotophor, or of dark and light portions in referring to the change in absorption characteristics brought about in a scotophor by suitable irradiation, it is to be understood that these changes in absorption may occur outside the visible spectrum. For example, irradiation of a scotophor which is visibly uncolored may cause the scotophor to absorb light in a portion of the non-visible spectrum, e.g., the. infra-red. This change in absorption characteristics can be detectedl by appropriate optical instruments, including those disclosed in this specification, although the change in the scotophor is unapparent to the eye. Although the terms colored or dark will be used in this specification for convenience in visualizing the invention, it is to be understood that these terms merely have reference to an absorption spectrum of an irradiated scotophor which differs from the absorption spectrum of a non-irradiated scotophor, although neither spectrum may absorb in the visible spectrum, i.e., show visible color.

, The radiation most appropriate for causing the production of color, either visible or in the sense defined just above, in tenebrescent materials is of high energy, for example, a-particles, gamma rays, cathode rays, X- rays, short wavelengths in the ultra-violet and near ultraviolet spectra between about 225-400 millimicrons, and the like. Erasing of a tenebrescent crystalthat is loss of the color produced by irradiation with short wavelengths-is best accomplished by radiation of the colored scotophor with a wavelength which is maximally absorbed by the colored scotophor.

These observations are in accord with theory, which holds that tenebrescence is associated with the appearance in imperfect crystals of defect energy levels between a filled band and the conduction band. Upon irradiaabsorption band of the colored scotophor, but to either side of, or to one side of, andl in the absence of, radiation containing or immediately surrounding a wavelength of peak absorption. For example, this principle can be illustrated by reference to a particular tenebrescent material, the mineral Hackmanite, NaCl(NaAlSiO4)3, which has a characteristic raspberry red color when activated by ultraviolet light, and which has a characteristic absorption spectrum in the colored state having a maximum in the visible at about 550 millimicrons. Production of the colored state in Hackmanite is conveniently brought about, for example by irradiation of the material with ultra-violet light of a wavelength below about 400 millimicrons, suitably between 225 and 400 millimicrons, and preferably as short a wavelength within this range as possible, since it has been discovered that the intensity of color in the scotophor is inversely dependent on the wavelength of the radiation employed. Thus, lwith reference to the ligure, if unit 11 contains Hackmanite as the tenebrescent substance., writer scanner means 12-13 suitably generate a modulated light beam 19 of ultra-violet light of the frequency earlier mentioned. However, other sources of high energy radiation can be employed.

Similarly, eraser-scanner means 14-15 suitably generate a modulated light beam 21 having a wavelength of about 550 millimicrons, for example, since this wavelength is of maximum eiiicacy in erasing the visible color of Hackmanite. Filter-Hoodlight combination 16-17 can be employed to illuminate unit 11 with light 22 of frequencies between about 555-700 and/or 450-545 millimicrons, for example. These wavelengths will reveal a discernible pattern of color 20 detectible by reader-scanner 18 since they are absorbed in part by Hackmanite in its radiated or colored state but not in its unirradiated and uncolored state, but will not cause appreciable bleaching or loss of color from `darkened portions 20 of unit 11. Generally, wavelengths longer ythan those of maximum absorption are preferred for reading, to avoid any possible interference with the short wavelengths used t write on scotophor-containing unit 11.

In an important embodiment of the invention, beam 22 is in the near infra-red and has a wavelength of about 2000 millimicrons. Hackmanite, in the colored or excited state has an absorption band at about this Wavet l length, which band is absent in the unexcited substance.

tion of a scotophor with -high energy radiation, electrons are raised from the iilled band to the conduction band, from whence they drop to the defect energy levels between the bands. Electron transitions from the defect bands to the conduction band (which involve a smaller energy change than do transitions between the lled band and the conduction band) change the absorption characteristics of the scotophor, i.e., result in the production of colon in the sense earlier dened. Irradiation of a colored scotophor containing electrons trapped in the defect energy levels with light of a wavelength maximally absorbed by the colored scotophor apparently raises the electrons from the defect energy levels to the conduction band, from which they return by non-radiative transitions to the lled band with loss of color in the scotophor.

Thus, in the use of visible light to detect the colored and uncolored portions of a scotophor, the presence of by illuminating the colored scotophor with light in the used to illuminate the excited material.

appreciable bleaching, but can be bleached with high intensity visible light. For example, Hackmanite does not show appreciable bleaching of the colored form when radiated with white light of 2 footcandles intensity for` periods of an hour or more, but will bleach to its colorless form when radiated with white light of about 800 footcandles intensity for about a minute. However, this system employing light beams of differing intensity is less convenient than that employing light beams of different wavelengths, since the control of wavelength, e.g. by filters, is far more convenient and sure than is regulation of beam intensity.

Although Hackmanite is a convenient tenebrescent material which occurs naturally or can be prepared synthetically, for example by the process of U.S. Patent 2,761,846 to Medved, granted May 28, 1952, numerous other tenebrescent materials can suitably be employed in the construction of storage unit 11. Thus, the alkali halides'` are scotophors. The absorption maxima (in millimicrons) and colors of some of the alkali halides are reported below in Table 1.

F Cl Br I Li 25? (I)I.V.) (color- 385 lt. yellow ess N a 340 lt. yellow 465 amber 540 violet.. 588 blue. K 455 yellow 563 blue violet..- 63%1deep 685 green.

Rb violet 610 blue 720 green- 775 (LR) b ue. (colorless). Cs green-blue 600 bhw lblend (ZnS), carbonate minerals such as calcite (CaCOa),

phosphates such as apatite [FCa5(PO4)3], sulfates such as langbeinite (K2SO4-2MgSO4), nitrates such as saltl[peter (NaNO3), cyanides such as NaCN, thiocyanates such as NH4SCN, borates, tungstates, and silicates such as spodume (LiAlSizOs), sodalite (3NaAlSiO4-NaC1), topaz [(FeOH)2Al2SiO4] and other minerals such as feldspar, mica, beryl, tourmaline, pyromorphite, cancrinite, calcocroite, brazilianite, phenakite, kunzite, scapolite, sapphite, oligoclase, lapis lazuli, and barytes are scotophors.

These materials can be activated in many cases by ultraviolet light, or can be doped with impurities to render them sensitive to ultra-violet. For example, KCl can be made ultra-violet sensitive by doping with NaOH, apatite by replacing some lluoride with chloride, sodalite by addition of chloride and sulfide, etc. In other cases, cathode rays, X-rays, or bombardment with nuclear particles can be used to produce the activated or colored state.

Although specic embodiments have been shown and described, it is to be understood that they are illustrative and are not to be construed as limiting on the scope and spirit of the invention.

I claim:

1. A system for the deposit, storage, and retrieval of information comprising storage means comprising a tenebrescent substance capable of exhibiting an unexcited state having a -lirst characteristic labsorption spectrum associated therewith and an excited state having a second, different, characteristic absorption spectrum associated therewith, writing means comprising a first modulated writing beam of radiation, adaptedto play on said-storage meansA and selectively exciting unexcited tenebrescent substance `and thereby changing its characteristic absorption spectrum, erasing means comprising a second modulated erasing beam of de-exciting radiation, adapted to play on said storage means and selectively de-exciting excited tenebrescent substance and thereby changing its characteristic absorption spectrum, and reading means compri-sing a third illuminating beam of radiation, vadapted to play on said storage means and neutral with respect to excitation and deexcit'ation of the tenebrescent substance, said illuminating beam being differently absorbed by -the excited and unexcited tenebrescent substance in said storage means and excluding radiation containing and immediately surrounding a wavelength of peak absorption of said excited tenevbres-cent substance, andmeans for detecting these differences in absorption of the illuminating beam.

2. A system asin claim 1 wherein said tenebrescent substance is opaque Iand the differences in absorption of the illuminating beam by said detecting means are detected by reflection of the illuminating beam from the opaque tenebrescent substance.

3. A system as in claim 1 wherein said tenebrescent substance is pellucid and the differences in absorption of the illuminating beam by said detecting means are detected by transmission of the illuminating beam through the pellucid tenebrescent substance.

4. A system for the deposit, storage, and retrieval of information comprising storage means comprising a tenebrescent substance capable of exhibiting an unexcited state having a first characteristic absorption spectrum associated therewith and an excited state having a second, different, characteristic absorption spectrum associated therewith, writing means comprising a irst modulated writing bea-m of electromagnetic radiation,

trum, and reading means comprising a third illuminating v beam of electromagnetic radiation adapted to play on said storage means and substantially neutral with respect to excitation and de-excita-tion of the tenebrescent substance, said illuminating beam being differently absorbed by the excited and unexcited tenebrescent substance in said storage means and excluding radiation containing and immediately surrounding a wavelength of peak absorption of said excited tenebrescent substance, and means for detecting these diierences in absorption of the illuminating beam.

5. A system as in claim 4 wherein said writing beam is a modulated beam of ultra-violet light.

6. A system as in claim 4 wherein said erasing beam is a modulated beam of light of a wavelength corresponding with the peak absorption wavelength of the tenebrescent substance in its excited form.

7. A system as in claim 4 wherein said. illuminating beam Hoods said storage means with light, and said detecting means scan said'storage means.

8. A system for the deposit, storage, and retrieval of information comprising storage means comprising a tenebrescent substance capable of exhibitingv an unexcited state having a first characteristic absorption spectrum associated therewith and a-n excited state having a second, different, characteristic absorption spectrum associated therewith, writing means comprising a first modulated writing beam of ultra-violet light, adapted to play on said storage means and selectively exciting unexcited tenebrescent substance and thereby changing its characteristic absorption spectrum, erasing means comprising a second modulated erasing beam of light of a wavelength corresponding with the peak absorption wavelength of the tenebrescent substance in its excited form and adapted to play on said storage means, and reading means comprising a third illuminating beam of light of wavelengths excluding the peak absorption wavelength of the tenebrescent substance in its excited form and adapted to play on s-aid'storage means, said illuminating beam being differently ab- 'sorbed by the excited and unexcited tenebrescent sub- 10. A system as in claim 8 wherein said tenebrescent substance is pellucid and the differences in absorption'of the illuminating beam by said detecting means are detected by transmission of the illuminatin-g beam through the pellucid tenebrescent substance.

11. A system as in claim 8 wherein said modulated writing beam and modulated erasing beam are scanning beams generated by cathode ray tubes.

12. A system as in claim 11 wherein said illuminating beam is a light beam ilooding said storage means, said light beam being filtered to remove peak absorption wavelengths of the excited tenebrescent substance, and said detecting means scan said storage means.

13. A system for the deposit, storage, and retrieval of information comprising storage means comprising tenebrescent Hackmanite, writing means comprising a rst modulated beam of ultra-violet light of a wavelength between about 25 0-400 millimicrons, adapted to play on said storage means and selectively coloring colorless Hackmanite thereby changing its absorption spectrum, erasing means comprising a second modulated beam of light of a wavelength of about 550 millimicrons, adapted to play on said storage means and selectively decolorizing colored Hackmanite thereby changing its absorption spectrum, and reading means comprising a third illuminating beam of li-ght, adapted to play on said storage means and of wavelengths excluding those wavelengths immediately surrounding and including 550 millimicrons, which illuminating wavelengths are differently absorbed by the colored and colorless Hackmlanite, and detecting means for detecting these differences in absorption.

14. A system as in claim 13 wherein said illuminating beam comprises 'wavelengths between about 450-700, excluding those wavelengths immediately surrounding and lincluding 550 millimicrons.

15. A system as in claim 13 wherein said illuminating beam has a wavelength of about 2000 millimicrons.

References Cited by the Examiner UNITED STATES PATENTS 2,432,908 12/ 1947 Leverenz 313-911 2,563,472 8/.1951 Leverenz 313-9'1 X DAVID J. GALVIN, Primary Examiner.

BENNETT G. MILLER, Examiner. v 

1. A SYSTEM FOR THE DESPOSIT, STORAGE, AND RETRIEVAL OF INFORMATION COMPRISING STORAGE MEANS COMPRISING A TENEBRESCENT SUBSTANCE CAPABLE OF EXHIBITING AN UNEXCITED STATE HAVING A FIRST CHARACTERISTIC ABSORPTION SPECTRUM ASSOCIATED THEREWITH AND AN EXCITED STATE HAVING A SECOND, DIFFERENT, CHARACTERISTIC ABSORPTION SPECTRUM ASSOCIATED THEREWITH, WRITING MEANS COMPRISING A FIRST MODULATED WRITING BEAM OF RADIATION, ADAPTED TO PLAY ON SAID STORAGE MEANS AND SELECTIVELY EXCITING UNEXCITED TENEBRESCENT SUBSTANCE AND THEREBY CHANGING ITS CHARACTERISTIC ABSORPTION SPECTRUM, ERASING MEANS COMPRISING A SECOND MODULATED ERASING BEAM OF DE-EXCITING RADIATION, ADAPTED TO PLAY ON SAID STORAGE MEANS AND SELECTIVELY DE-EXCITING EXCITED TENEBRESCENT SUBSTANCE AND THEREBY CHANGING ITS CHARACTERISTIC ABSORPTION SPECTRUM, AND READING MEANS COMPRISING A THIRD ILLUMINATING BEAM OF RADIATION, ADAPTED TO PLAY ON SAID STORAGE MEANS AND NEUTRAL WITH RESPECT TO EXCITATION AND DEEXCITATION OF THE TENEBRESCENT SUBSTANCE, SAID ILLUMINATING BEAM BEING DIFFERENTLY ABSORBED BY THE EXCITED AND UNEXCITED TENEBRESCENT SUBSTANCE IN SAID STORAGE MEANS AND EXCLUDING RADIATION CONTAINING AND IMMEDIATELY SURROUNDING A WAVELENGTH OF PEAK ABSORPTION OF SAID EXCITED TENEBRESCENT SUBSTANCE, AND MEANS FOR DETECTING THESE DIFFERENCES IN ABSORPTION OF THE ILLUMINATING BEAM. 